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UMOUNT(8)                    System Administration                   UMOUNT(8)

NAME
       umount - unmount file systems
SYNOPSIS
       umount [-hV]
       umount -a [-dflnrv] [-t vfstype] [-O options]
       umount [-dflnrv] {dir|device}...
DESCRIPTION
       The  umount command detaches the file system(s) mentioned from the file
       hierarchy.  A file system is specified by giving the directory where it
       has  been  mounted.  Giving the special device on which the file system
       lives may also work, but is obsolete, mainly because it  will  fail  in
       case this device was mounted on more than one directory.
       Note  that  a  file  system cannot be unmounted when it is 'busy' - for
       example, when there are open files on it, or when some process has  its
       working  directory  there,  or  when  a swap file on it is in use.  The
       offending process could even be umount itself - it opens libc, and libc
       in  its  turn may open for example locale files.  A lazy unmount avoids
       this problem, but it may introduce another issues. See --lazy  descrip-
       tion bellow.
OPTIONS
       -a, --all
              All  of  the  file systems described in /etc/mtab are unmounted.
              (With umount version 2.7 and later: the proc filesystem  is  not
              unmounted.)
       -A, --all-targets
              Unmount  all mountpoints in the current namespace for the speci-
              fied filesystem.  The filesystem could be specified  by  one  of
              the  mountpoints  or  device  name  (or UUID, etc.). This option
              could be used together with --recursive then all  nested  mounts
              within the filesystem are recursively unmounted.
       -c, --no-canonicalize
              Do  not  canonicalize paths.  For more details about this option
              see the mount(8) man page.
       -d, --detach-loop
              When the unmounted device was a loop device, also free this loop
              device.  This  option  is unnecessary for devices initialized by
              mount(8), in this case "autoclear" functionality is  enabled  by
              default.
       --fake Causes  everything to be done except for the actual system call;
              this 'fakes' unmounting the  filesystem.   It  can  be  used  to
              remove  entries  from /etc/mtab that were unmounted earlier with
              the -n option.
       -f, --force
              Force unmount (in case of an unreachable NFS system).  (Requires
              kernel 2.1.116 or later.)
       -i, --internal-only
              Do  not  call  the  /sbin/umount.<filesystem>  helper even if it
              exists.  By default /sbin/umount.<filesystem> helper  is  called
              if one exists.
       -n, --no-mtab
              Unmount without writing in /etc/mtab.
       -l, --lazy
              Lazy unmount.  Detach the filesystem from the filesystem hierar-
              chy now, and cleanup all references to the filesystem as soon as
              it is not busy anymore.  (Requires kernel 2.4.11 or later.)
              A system reboot would be expected in near future if you're going
              to use this option for network filesystem  or  local  filesystem
              with  submounts.   The  recommended use-case for umount -l is to
              prevent hangs on shutdown due to an  unreachable  network  share
              where a normal umount will hang due to a downed server or a net-
              work partition. Remounts of the share will not be possible.

       -O, --test-opts options,list
              Indicate that the actions should only be taken on  file  systems
              with  the specified options in /etc/fstab.  More than one option
              type may be specified in a comma separated  list.   Each  option
              can  be  prefixed with no to specify options for which no action
              should be taken.
       -R, --recursive
              Recursively unmount each directory specified. Recursion for each
              directory  will stop if any unmount operation in the chain fails
              for any reason. The relationship between mountpoints  is  deter-
              mined  by  /proc/self/mountinfo  entries. The filesystem must be
              specified by mountpoint path, recursive unmount by  device  name
              (or UUID) is unsupported.
       -r, --read-only
              In case unmounting fails, try to remount read-only.
       -t, --types vfstype,ext2,ext3
              Indicate  that  the actions should only be taken on file systems
              of the specified type.  More than one type may be specified in a
              comma separated list.  The list of file system types can be pre-
              fixed with no to specify the  file  system  types  on  which  no
              action should be taken.
       -v, --verbose
              Verbose mode.
       -h, --help
              Print help message and exit.
       -V, --version
              Print version and exit.
THE LOOP DEVICE
       The  umount  command  will  automatically detach loop device previously
       initialized by mount(8) command independently of /etc/mtab.
       In this case the device is initialized with "autoclear" flag (see  los-
       etup(8)  output  for more details), otherwise it's necessary to use the
       option  --detach-loop or call losetup -d <device>. The  autoclear  fea-
       ture is supported since Linux 2.6.25.
NOTES
       The syntax of external umount helpers is:
       /sbin/umount.<suffix> {dir|device} [-nlfvr] [-t type.subtype]
       where  the  <suffix>  is  filesystem type or a value from "uhelper=" or
       "helper=" mtab option.  The -t option is used for filesystems with sub-
       types support (for example /sbin/mount.fuse -t fuse.sshfs).
       The  uhelper= (unprivileged umount helper) is possible to use when non-
       root user wants to umount a mountpoint which  is  not  defined  in  the
       /etc/fstab file (e.g. devices mounted by udisk).
       The   helper=  mount  option  redirects  all  umount  requests  to  the
       /sbin/umount.<helper> independently on UID.
FILES
       /etc/mtab table of mounted file systems
ENVIRONMENT
       LIBMOUNT_FSTAB=<path>
              overrides the default location of the fstab file
       LIBMOUNT_MTAB=<path>
              overrides the default location of the mtab file
       LIBMOUNT_DEBUG=0xffff
              enables debug output
SEE ALSO
       umount(2), mount(8), losetup(8)
HISTORY
       A umount command appeared in Version 6 AT&T UNIX.
AVAILABILITY
       The umount command is part of the util-linux package and  is  available
       from  Linux  Kernel Archive <ftp://ftp.kernel.org/pub/linux/utils/util-
       linux/>.

util-linux                        August 2012                        UMOUNT(8)